The present invention relates generally to innovations and improvements in the quantitative analysis of components within a material and is especially suited to the analysis of the fat content of meats.
Using X-ray beams to determine relative amounts of components within materials, such as the quantity of fat within meat, are known, for example, from Madigan U.S. Pat. No. 2,992,332, which deals with determining the quantitative relationship between meat components by measuring gamma ray penetration thereof. Systems of this type use a single, polychromatic radiation beam, and they are limited in their usefulness by the need to first obtain a sample of the material being analyzed which is of a uniform predetermined weight and then to mold that sample to a predetermined uniform size having a precise geometrical configuration. Developments such as these recognize that one of the components in a particular system has an effective atomic number greater than that of another component; for example, in meat, lean meat has a high concentration of moisture and protein and includes nitrogen and oxygen atoms which are of a greater atomic number than the carbon and hydrogen atoms which predominate in the fat component, meaning that the lean meat component absorbs gamma radiation to a far greater extent than does the fat component when the gamma rays are within that range where the X-ray energy incident upon the meat is attenuated as a result of a phenomenon known as the photoelectric effect.
Copending U.S. Ser. No. 843,702, filed Oct. 19, 1977 by William H. Groves and Andrew E. Donovan for Two-Level X-Ray Analysis for Determining Fat Percentage, herein incorporated by reference, recognizes the previously known general principle that beam attenuation measurements may be conducted at two different energy levels, rather than at a single level when using monochromatic beams. Monochromatic beams are usually generated by radioactive nuclides or radionuclides, which are released as an electron moves from one atomic "shell" to another. Monochromatic beams are very easy to characterize especially when compared with polychromatic beams, such as the X-rays generated by Coolidge tubes.
Polychromatic beams result in a continuous energy spectrum characterized by the excitation potential applied to the tube, sometimes producing secondary radiation which may have a different energy spectrum and a different direction of propagation relative to the primary beam. As a polychromatic beam passes through a sample, its intensity is attenuated with the lower energy fraction of the beam being attenuated to the highest degree, causing a continuous change in the average energy level of the beam as it passes through increasing sample thicknesses, which is a well-recognized effect referred to as "beam hardening" and is considered to be one of the major disadvantages in attempting to use polychromatic beams in X-ray absorptiometry. Said copending application of Groves and Donovan describes the use of polychromatic beams at two different energy levels in a manner which significantly reduces inaccuracies resulting from the "beam hardening" effect.
There exists a significant need for avoiding the inflexibility of systems such as Madigan which are most advantageously used in the random sampling of products capable of being molded, one of the most common uses being in evaluating the fat content of ground meat formulations. This need is not completely fulfilled by Groves and Donovan, which affords significantly increased flexibility over Madigan because Groves and Donovan can analyze heterogenous materials having non-uniform weights and sizes so long as they have relatively smooth surfaces.
The present invention overcomes the disadvantages of inflexibility in the single energy level devices while at the same time eliminating the need of Groves and Donovan to smooth the material being analyzed if it does not have relatively smooth surfaces, meaning that the present invention provides a rapid, accurate and non-destructive means and method of analysis that requires no sample preparation, calls for only a minimum of sample handling, and can be used on meat that is fresh or frozen and that has been boxed or bagged at the meat packing plant level.
It is accordingly a general object of the present invention to provide an improved means for determining the relative quantities of the components of a heterogeneous material.
Another object of the present invention is an improved method and apparatus using polychromatic beams at three or more different energy levels in order to analyze the content of the components in a primarily two-component material.
Another object of this invention is an improved method and apparatus utilizing three different energy levels for determining the fat content of meat products having variable physical properties, primarily as embodied by the density and thickness of the various samples, as well as having surface roughness.
Another object of this invention is an improved method and apparatus utilizing four different energy levels for the fat content of meat products having variable physical properties, as well as having surface roughness and variable fat distribution.
Another object of the present invention is an improved method and apparatus which can be operated by relatively unskilled labor and under plant operation conditions by scanning meats that are sold as commodity items.
Another object of the present invention is an improved method and apparatus which includes calibration standards at three or more energy levels for accurately and automatically determining the fat content of primarily two-component materials such as meat.